雷射干涉重力波觀測站(Laser Interferometer Gravitational wave Observatory, LIGO)架設大型麥克森干涉儀用於探測重力波。由於重力波訊號極其微弱，故降低量測雜訊與提升量測靈敏度相當重要。為了提升量測的靈敏度，不僅需要降低高反射鏡的熱擾動雜訊(Coating Brownian noise)，也需具備良好的光學性質，因此本實驗重點在於降低薄膜的機械損耗與光學吸收。
由於先前研究發現PECVD所鍍製之氮化矽薄膜含有氫的存在，其原因為製程氣體含有氫，故鍍製出的氮化矽薄膜含有Si-H鍵及N-H鍵。Si-H鍵會在室溫下貢獻機械損耗，N-H鍵則會在低溫下產生損耗峰值和貢獻在波段1550nm的光學吸收。因此筆者採用製程氣體與靶材皆不含氫的IBS(Ion Beam Sputter)鍍製氮化矽薄膜，預期鍍製出不含氫的氮化矽薄膜。IBS製程方法為氮離子束轟擊矽靶鍍製氮化矽薄膜，其中腔體不通入製程氣體進行反應。筆者透過調變Beam voltage來調製薄膜光學與材料特性，並量測不同製程參數下所鍍製之薄膜的氫鍵結濃度、Silicon dangling bond、光學吸收、XPS以及金屬汙染物含量，並將其統整進行深入探討。
本實驗結果顯示，影響光學吸收之矽懸鍵與金屬汙染物皆與製程參數Beam voltage存在一定關係。隨著Beam voltage降低，薄膜內的Silicon dangling bond濃度下降，然而金屬汙染物含量卻是隨著Beam voltage降低而增加。由於上述兩項因子皆會影響薄膜光學吸收，導致Beam voltage與薄膜消光係數不存在一定趨勢。研究更發現，隨著通入離子源之冷卻水溫降低，薄膜內金屬汙染物含量隨之下降。但水溫降到一定程度時，薄膜內金屬汙染物含量降幅驟緩。另外由FTIR與XPS之數據結果顯示，薄膜成份裡含有氫與氧，推測二者來源是來自基板附近之不鏽鋼壁上吸附的水氣所貢獻。

The Laser Interferometer Gravitational-Wave Observatory (LIGO) established a large-scale Michelson interferometer to detect gravitational waves. Since the gravitational wave signal is extremely weak, it is crucially important to reduce the measurement noise and increase the measurement sensitivity. In order to enhance the measurement sensitivity, we reduce the coating thermal noise and improve optical properties on the high reflective mirror. Therefore, the primary point of experiment is to reduce the mechanical loss and optical absorption of the film.
From the previous research, we had found that the silicon nitride film which was deposited by PECVD contained Si-H bonds and N-H bonds because the process gas contained hydrogen. The Si-H bonds contributed the mechanical loss at room temperature, then the N-H bonds generated loss at low temperature and contributed the optical absorption at the 1550 nm. Therefore, we used IBS (Ion Beam Sputter) to deposit the silicon nitride film because the process gas and the target did not contain hydrogen. Besides, we adjusted the optical and material properties of the film by modulating the beam voltage. Furthermore, we measured the Si-H bonds, N-H bonds, silicon dangling bond, optical absorption, atomic proportion, and the metal contaminants in the film.
The results from measurement showed that the silicon dangling bonds and metal contaminants affect the optical absorption, and they have certain relationship with beam voltage. As the beam voltage reduced, the concentration of silicon dangling bond decreased. However, content of metal contaminants content increased. Then, because silicon dangling bonds and metal contaminants had an influence on the optical absorption, there was obvious trend in beam voltage and extinction coefficient of film. According to the reference and results of measurement, when the temperature of cooling water which supplied to the ion source decreased, the content of metal contaminants decreased. In addition, we found that there were hydrogen and oxygen in the film from the results of FTIR and XPS. Then we speculated that the source of hydrogen and oxygen was water vapor which adsorbed on the stainless-steel wall near the substrate.

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